1. Field of the Invention
The present invention relates to a torque converter for vehicles, and more particularly, to an improvement thereof for improving the fuel consumption of a vehicle by decreasing power loss at the torque converter in its operation at and around the fluid coupling condition attained after a substantial completion of torque conversion, the improvement being accomplished by optimizing the aerofoil and the array configuration of stator vanes such that a separation of working fluid on the surface of the stator vanes is suppressed.
2. Description of the Related Art
In the torque converter having a fluid circulation system in which a working fluid circulates through a pump, a turbine and a stator (hydrodynamic type torque converter), the flow of working fluid discharged from the turbine is returned to the pump through a deflection applied by the stator, whereby the ratio of the torque of the turbine, i.e. torque output means, to that of the pump, i.e. torque input means, is continuously changed from a predetermined maximum value to a value close to 1, as the ratio of the rotation speed of the turbine to that of the pump rises up from zero, as well known m the art. Further, in the case of the torque converter assembled in the drive system of a vehicle, the torque converter operates such that, after it has completed the torque conversion operation of first magnifying the wheel driving torque at a certain maximum ratio and then gradually and steplessly decreasing the vehicle driving torque so as to provide a smooth start-up and acceleration of the vehicle, thereafter it operates, for the most part of the operation period thereof, as a fluid coupler in which the turbine rotates at a rotation speed slightly lower than that of the pump due to a slippage unavoidable to transmit the coupling torque therebetween.
Since the torque converter of the vehicle is thus generally operated in the fluid coupling condition, it is expected that, if the power loss of the torque converter during its fluid coupling operation is decreased, the fuel consumption of the vehicle is correspondingly improved.
A general example of the aerofoil and the array configuration of the stator vanes of the torque converter for vehicles is shown in FIG. 1, together with a general pattern of the flow of working fluid, flowing across the array of stator vanes, in the fluid coupling condition of the torque converter. In FIG. 1, the stator 10 includes stator vanes 12, 14, 16 and so on, positioned between a diagrammatically shown array of turbine blades 18 and a diagrammatically shown array of pump blades 20, to introduce the flow of working fluid discharged from the array of turbine blades to the array of pump blades by applying a deflection thereto. Although there is a certain disturbance in the flow of working fluid moving from the outlet of the array of turbine blades to the stator 10 and also in the flow of working fluid moving from the stator to the inlet of the array of pump blades 20, since the inlet and the outlet stream line of the working fluid to and from each of the array of stator vanes are generally maintained stable such as shown by inlet stream lines 22, 24 and 26 and outlet stream lines 28, 30 and 32 with respect to the vanes 12, 14 and 16, the flow of working fluid moving through a space between each two adjacent vanes such as 12 and 14 may be handled as a flow of working fluid 32 corresponding to a space portion hatched in the figure.
Referring to the flow of working fluid 32, a separation of the working fluid would occur at: a portion 34 of the pressure side surface of the vane 12 located adjacent to the leading edge thereof where the suppression of separation of the working fluid by the adjacent vane 14 is hardly effected; and a portion 36 of the suction side surface of the vane 14 located adjacent the trailing edge thereof where the suppression of separation of the working fluid by the adjacent vane 12 is hardly effected.
With respect to the surface portion 34, it is considered that whether a separation of the working fluid occurs or not at this surface portion is affected by the effect of the pressure side surface of the vane 12 adjacent the leading edge thereof against the change of the width of the passage presented for the flow of working fluid 32 and the angle made by the surface portion 34 with respect to the flow of working fluid 32, whereas, with respect to the surface portion 36, it is considered that whether a separation of working fluid occurs or not at this surface portion is affected by the effect of the suction side surface of the vane 14 adjacent the trailing edge thereof against the change of the width of the passage presented for the flow of working fluid 32 and the angle made by the surface portion 36 with respect to the flow of working fluid 32.